Colorbar

The pygmt.Figure.colorbar method creates a color scalebar. The colormap is set via the cmap parameter. A full list of available color palette tables can be found at https://docs.generic-mapping-tools.org/6.5/reference/cpts.html. Use the frame parameter to add labels to the x and y axes of the colorbar by appending +l followed by the desired text. To add and adjust the annotations (a) and ticks (f) append the letter followed by the desired interval. The placement of the colorbar is set via the position parameter. There are the following options:

• j/J: placed inside/outside the plot bounding box using any 2-character combination of vertical (Top, Middle, Bottom) and horizontal (Left, Center, Right) alignment codes, e.g. position="jTR" for Top Right.

• g: using map coordinates, e.g. position="g170/-45" for longitude 170° East, latitude 45° South.

• x: using paper coordinates, e.g. position="x5c/7c" for 5 cm, 7 cm from anchor point.

• n: using normalized (0-1) coordinates, e.g. position="n0.4/0.8".

Note that the anchor point defaults to Bottom Left (BL). Append +h to position to get a horizontal colorbar instead of a vertical one (+v).

import pygmt

fig = pygmt.Figure()
fig.basemap(region=[0, 3, 6, 9], projection="x3c", frame=["af", "WSne+tColorbars"])

# ============
# Create a colorbar designed for seismic tomography - roma
# Colorbar is placed at Bottom Center (BC) by default if no position is given
# Add quantity and unit as labels ("+l") to the x and y axes
# Add annotations ("+a") in steps of 0.5 and ticks ("+f") in steps of 0.1
fig.colorbar(cmap="roma", frame=["xa0.5f0.1+lVelocity", "y+lm/s"])

# ============
# Create a colorbar showing the scientific rainbow - batlow
fig.colorbar(
    cmap="batlow",
    # Colorbar positioned at map coordinates (g) longitude/latitude 0.3/8.7,
    # with a length/width (+w) of 4 cm by 0.5 cm, and plotted horizontally (+h)
    position="g0.3/8.7+w4c/0.5c+h",
    box=True,
    frame=["x+lTemperature", "y+l°C"],
    scale=100,
)

# ============
# Create a colorbar suitable for surface topography - oleron
fig.colorbar(
    cmap="oleron",
    # Colorbar placed outside the plot bounding box (J) at Middle Right (MR),
    # offset (+o) by 1 cm horizontally and 0 cm vertically from anchor point,
    # with a length/width (+w) of 7 cm by 0.5 cm and a box for NaN values (+n)
    position="JMR+o1c/0c+w7c/0.5c+n+mc",
    # Note that the label 'Elevation' is moved to the opposite side and plotted
    # vertically as a column of text using '+mc' in the position parameter
    # above
    frame=["x+lElevation", "y+lm"],
    scale=10,
)

# ============
# Create a colorbar suitable for categorical data - hawaii
# Set up the colormap
pygmt.makecpt(
    cmap="hawaii",
    series=[0, 3, 1],
    # Comma-separated string for the annotations of the colorbar
    color_model="+cA,B,C,D",
)
# Plot the colorbar
fig.colorbar(
    cmap=True,  # Use colormap set up above
    # Colorbar placed inside the plot bounding box (j) in the Bottom Left (BL) corner,
    # with an offset (+o) by 0.5 cm horizontally and 0.8 cm vertically from the anchor
    # point, and plotted horizontally (+h)
    position="jBL+o0.5c/0.8c+h",
    box=True,
    # Divide colorbar into equal-sized rectangles
    equalsize=0.5,
)

fig.show()